The present invention relates generally to semiconductor packaging and, more particularly, to a die mounting substrate that has electrically isolated bond pads.
Packaged semiconductors provide external electric connections and physical protection for packaged semiconductor dies. Continued progress in reduction of the size of the semiconductor dies and increased functionality and complexity of the electronic circuits integrated in the dies requires size reduction of the packaging with the same or greater complexity of the electrical connections with external circuits.
One typical type of packaged semiconductors is Quad Flat Pack (QFP) packages, which are formed with a semiconductor die mounted to a lead frame. The lead frame is formed from a sheet of metal that comprises a die attach pad often called a flag and arms that attach the flag to a frame. Leads or lead fingers of the lead frame are electrically connected to electrodes of the die with bond wires. The leads extend outside of a package body and can be connected to external circuitry. After the electrodes and leads are connected, the semiconductor die and inner parts of the leads are encapsulated in a compound (material) such as a plastic material leaving only outer sections of the leads exposed. These exposed sections are cut from the frame of the lead frame (singulated) and bent for ease of connection to a circuit board. However, the inherent structure of QFP packages results in limiting the number of leads, and therefore the number of package external electrical connections, that can be used for a specific QFP package size. Further, the external electrical connections of the lead frame based grid array packages are typically fabricated from a thin single sheet of conductive material, such as copper or aluminium, and these connections may not be sufficiently held within the encapsulating compound (material) and may become lose.
An alternative to lead frames in the assembly of semiconductor devices is the use of circuit substrates. These substrates have internal and external bond pads that are interconnected typically by vias and runners; therefore these substrates resemble miniature Printed Circuit Boards (PCBs). Semiconductor device assembly with such substrates typically includes directly mounting a semiconductor die on the substrate and then connecting electrodes of the die to substrate bonding pads (the internal bond pads) with bond wires and then encapsulating the die and bond wires with a molding compound. The external mounting pads provide external connections as a grid array that are typically mounted to a larger circuit substrate such as a PCB or similar structure.
Semiconductor die packages are often assembled with an increased functionality and thus results in an increase in the number of required bond pads. This increase in the number of required bond pads may necessitate an increased footprint or die size, and overall package size, in order to comply with packaging rules such as: maximum and minimum allowable bond wire height; minimum bond site spacing; and maximum bend angle of a bond wire. In view of at least these packaging rules, each new semiconductor die typically has a corresponding customised substrate, which adds to the cost of the overall package. Thus, it would be advantageous to have a substrate that can accommodate various size dies and with varying numbers of electrodes/bond pads.